DC1871A - Linear Technology

LTC2995

2995f

TYPICAL APPLICATION

FEATURES DESCRIPTION

Temperature Sensor and

Dual Voltage Monitor with

Alert Outputs

The LTC

2995 is a high accuracy temperature sensor

and dual supply monitor. It converts the temperature of

an external diode sensor and/or its own die temperature

to an analog output voltage while rejecting errors due to

noise and series resistance. Two supply voltages and the

measured temperature are compared against upper and

lower limits set with resistive dividers. If a threshold is

exceeded, the device communicates an alert by pulling

low the correspondent open drain logic output.

The LTC2995 gives ±1°C accurate temperature results

using commonly available NPN or PNP transistors or

temperature diodes built into modern digital devices. Volt-

ages are monitored with 1.5% accuracy. A 1.8V reference

output simplifies threshold programming and can be used

as an ADC reference input.

The LTC2995 provides an accurate, low power solution for

temperature and voltage monitoring in a compact 3mm ×

3mm QFN package.

Dual OV/UV Supply and Single OT/UT Remote Temperature Monitor

APPLICATIONS

n Monitors Temperature and Two Voltages

n Voltage Output Proportional to Temperature

n Adjustable Thresholds for Temperature and Voltage

n ±1°C Remote Temperature Accuracy

n ±2°C Internal Temperature Accuracy

n ±1.5% Voltage Threshold Accuracy

n 3.5ms Update Time

n 2.25V to 5.5V Supply Voltage

n Input Glitch Rejection

n Adjustable Reset Timeout

n 220A Quiescent Current

n Open Drain Alert Outputs

n Available in 3mm × 3mm QFN Package

n Network Servers

n Core, I/O Voltage Monitors

n Desktop and Notebook Computers

n Environmental Monitoring L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

VPTAT vs Remote

Diode Temperature

REMOTE DIODE TEMPERATURE (°C)

–50

0.8

VPTAT (V)

1.0

1.2

1.4

050

100 150

2995 TA01b

1.6

1.8

–25 25 75 125

VCC

VH1

VL1

VH2

VL2

VPTAT

TO2

TO1

D+

D–

LTC2995

2.5V

1.2V

0.1µF

64.4k

10.2k

45.3k

2995 TA01a

VT1VT2 GND TMRVREF

20k 20k 140k

470pF

TEMPERATURE

SENSOR

ASIC

SYSTEM

MONITOR

OT T > 125°C

4mV/K

UT T < 75°C

+10%

–10%

45.3k

10.2k

194k

5nF

LTC2995

2995f

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS

(Notes 1, 2)

20 19 18 17 16

7 8

TOP VIEW

UD PACKAGE

20-LEAD (3mm × 3mm) PLASTIC QFN

910

VL1

VH2

VL2

VT2

VT1

TO2

T01

VREF

VH1

GND

TMR

D+

D–

VPTAT

VCC

GND

TJMAX = 150°C, θJA = 59°C/W

EXPOSED PAD PCB GROUND CONNECTED OPTIONAL

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VCC Supply Voltage l2.25 5.5 V

UVLO Supply Undervoltage Lockout Threshold VCC Falling l1.7 1.9 2.1 V

ICC Average Supply Current l220 300 µA

Temperature Measurement

VREF Reference Voltage LTC2995

LTC2995C

LTC2995I

LTC2995H

1.797

1.793

1.790

1.787

1.8

1.803

1.804

1.807

1.808

VREF Load Regulation ILOAD = ±200A l±1.5 mV

Remote Diode Sense Current –8 –192 µA

ORDER INFORMATION

VCC .............................................................. –0.3V to 6V

TMR, D+, D–, DS, PS, VPTAT, VREF ........ –0.3V to VCC + 0.3V

UV, OV, TO1, T02 .......................................... –0.3V to 6V

VH1, VL1, VH2, VL2, VT1, VT2 ..................... –0.3V to 6V

Operating Ambient Temperature Range

LTC2995C ................................................ 0°C to 70°C

LTC2995I .............................................–40°C to 85°C

LTC 2995H ......................................... –40°C to 125°C

Storage Temperature Range ..................–65°C to 150°C

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC2995CUD#PBF LTC2995CUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C

LTC2995IUD#PBF LTC2995IUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C

LTC2995HUD#PBF LTC2995HUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN –40°C to 125°C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.

LTC2995

2995f

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: All currents into pins are positive; all voltages are referenced to

GND unless otherwise noted.

Note 3: Remote diode temperature, not LTC2995 temperature.

Note 4: Guaranteed by design and test correlation.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Tconv Temperature Update Interval l3.5 5 ms

KTVPTAT Slope Ideality Factor η = 1.004 4mV/K

VPTAT Load Regulation ILOAD = ±200A ±1.5 mV

Tint Internal Temperature Accuracy

TAMB = –40°C to 125°C

±0.5

±2

±1 °C

°C

TRMT Remote Temperature Error, η = 1.004 0°C to 85°C (Notes 3, 4)

–40°C to 0°C (Notes 3, 4)

85°C to 125°C (Notes 3, 4)

±0.25

±1

±1.5

°C

Temperature Noise 0.15

0.01

°CRMS

°CRMS/√Hz

TVCC Temperature Error vs Supply l±0.5 °C/V

TRS Series Resistance Cancellation Error RSERIES = 100 l±0.25 ±1 °C

Temperature and Voltage Monitoring

VUOT Undervoltage/Overvoltage Threshold l492 500 508 mV

TOFF VT1, VT2 Offset l–3 –1 1 °C

∆THYST VT1, VT2 Temperature Hysteresis l2 5 10 °C

tUOD UV, OV Input 5mV Above/Below Threshold l0.5 2 ms

IIN VH1, VL1, VH2, VL2, VT1, VT2, Input Current l±20 nA

tUOTO UV/OV Time-Out-Period CTMR = TMR Open

CTMR = 1nF l5

0.5

10 20

ITMR TMR Current l±2.5 µA

Three State Pins DS, PS

VDS,PS(H,TH) PS, DS Input High Threshold lVCC – 0.4 VCC – 0.1 V

VDS,PS(H,TL) PS, DS Input Low Threshold l0.1 0.4 V

IDS,PS(IN,HL) PS, DS High, Low Input Current DS, PS at 0V or VCC l±4 µA

IDS,PS(IN,Z) Allowable Leakage Current l±1 µA

Digital Outputs

VOH High Level Output Voltage,

TO1, TO2, UV, OV

I = –0.5A lVCC – 1.2 V

VOL Low Level Output Voltage,

TO1, TO2, UV, OV

I = 3mA l0.4 V

LTC2995

2995f

TIMING DIAGRAMS

VLn

VUOT

tUOD tUOTO

2995 TD02

VHn

VUOT

tUOD tUOD

2995 TD03

VLn

VUOT

tUOD tUOD

2995 TD04

VHn Monitor Timing

VHn Monitor Timing (TMR Pin Strapped to VCC)

VLn Monitor Timing

VLn Monitor Timing (TMR Pin Strapped to VCC)

VHn

VUOT

tUOD tUOTO

2995 TD01

LTC2995

2995f

TYPICAL PERFORMANCE CHARACTERISTICS

Remote Temperature Error

vs Series Resistance

Remote Temperature Error

vs CDECOUPLE (Between D+ and D–)

Temperature Error with LTC2995 at

Same Temperature as Remote Diode

Remote Temperature Error

vs Ambient Temperature

Internal Temperature Error

vs Ambient Temperature

UVLO vs Temperature

VCC Rising, Falling

Buffered Reference Voltage

vs Temperature

Temperature Error vs Supply

Voltage

VPTAT Noise vs Averaging Time

TA = 25°C, VCC = 3.3V unless otherwise noted.

TA (°C)

–50

–3

TINT ERROR (°C)

–2

–1

75 150100

2995 G03

–25 0 25 50 125

TA (°C)

–50

–3

TRMT ERROR (°C)

–2

–1

75 150100

2995 G01

–25 0 25 50 125

TINTERNAL = TREMOTE

TA (°C)

–50

–3

TRMT ERROR (°C)

–2

–1

75 150100

2995 G02

–25 0 25 50 125

TREMOTE = 25°C

SERIES RESISTANCE ()

–6

ERROR (°C)

–4

–2

800600

2995 G05

200 400 12001000

DECOUPLE CAPACITOR (nF)

ERROR (°C)

–2

–4

–6 86

2995 G06

24 10

TA (°C)

–50

UVLO (V)

1.8

2.0

1.6 25 75 150

2995 G08

2.2

0–25 50 100 125

VCC RISING

VCC FALLING

TA (°C)

1.790

VREF (V)

1.795

2995 G09

1.800

1.810

1.805

–50 25 75 150

0–25 50 100 125

VCC (V)

ERROR (°C)

–0.2

–0.4

–0.6 35

2995 G04

0.2

0.6

0.4

246

AVERAGING TIME (ms)

0.01

VPTAT NOISE (°C RMS)

0.05

0.15

0.20

0.10

11000100

2995 G07

0.1 10

LTC2995

2995f

TYPICAL PERFORMANCE CHARACTERISTICS

Supply Current vs Temperature

Load Regulation of VPTAT –

Voltage vs Current

Single Wire Remote Temperature

Error vs Ground Noise

Load Regulation of VREF –

Voltage vs Current

TA = 25°C, VCC = 3.3V unless otherwise noted.

Delay vs Comparator Overdrive

UV, OV, TO1, TO2 vs Output Sink

Current

Reset Timeout Period

vs Capacitance

OVERDRIVE (mV)

DELAY (µs)

200

110

2995 G13

800

600

400

1200

1000

100

FREQUENCY (kHz)

0.1

0.01

ABSOLUTE TEMPERATURE ERROR (°C)

0.1

110 1000

2995 G12

100

VAC = 50mVP-P

TMR PIN CAPACITANCE (nF)

RESET TIMEOUT tUOTO (ms)

0.1 1 10 100

2995 G15

100

10000

1000

I (mA)

VUV/OV/TO1/TO2 (V)

0 5 10 15 20 25 30

2995 G14

0.6

0.4

0.2

0.8

LOAD CURRENT (mA)

1.78

VREF (V)

1.80

1.79

2995 G10

1.82

1.81

–4 –2 2 4

VCC = 2.25V

VCC = 3.5V

VCC = 4.5V

VCC = 5.5V

LOAD CURRENT (mA)

–4

1.14

VPTAT (V)

1.18

1.16

–2 0 4

2995 G11

1.20

1.22

VCC = 2.25V

VCC = 3.5V

VCC = 4.5V

VCC = 5.5V

SUPPLY CURRENT (µA)

240

230

220

2995 G16

250

TA (°C)

–50

200

210

50 100

–25 0 25 75 125 150

LTC2995

2995f

PIN FUNCTIONS

D+: Diode Sense Current Source. D+ sources the remote

diode sensing current. Connect D+ to the anode of the re-

mote sensor device. It is recommended to connect a 470pF

bypass capacitor between D+ and D–. Larger capacitors

may cause settling time errors (see Typical Performance

Characteristics). If D+ i s t i e d t o V CC, the LTC2995 measures

the internal sensor temperature. Tie D+ to VCC if unused.

D–: Diode Sense Current Sink. Connect D– to the cathode

of the remote sensor device. Tie D– to GND for single

wire remote temperature measurement (see Applications

Information) or internal temperature sensing.

DS: Diode Select Input. Three state pin that selects tem-

perature sensor location. Tie DS to VCC to monitor the

temperature of the internal diode or to GND to monitor the

temperature of the external diode. When DS is left uncon-

nected, the LTC2995 monitors both sensors alternately.

If D+ is tied to VCC, the LTC2995 measures the internal

sensor temperature regardless of the state of DS.

Exposed Pad: Exposed pad may be left open or soldered

to GND for better thermal coupling.

GND: Device Ground

OV: Overvoltage Logic Output. Open drain logic output

that pulls to GND when either the voltage at VL1 or VL2

is above 0.5V. Held low for a programmable delay time

set by the capacitor connected to pin TMR. OV has a weak

400k pull-up to VCC and may be pulled above VCC using

an external pull-up. Leave OV open if unused.

PS: Polarity Select Input. Selects the polarity of tempera-

ture thresholds VT1 and VT2. Connect PS to VCC to config-

ure VT1 as undertemperature and VT2 as overtemperature

threshold. Leave PS unconnected to configure both VT1

and VT2 as overtemperature thresholds. Connect PS to

GND to configure both VT1 and VT2 as undertemperature

thresholds. Tie to VCC if temperature thresholds are unused.

TMR: Reset Delay Timer. Attach an external capacitor

(CTMR) to GND to set the delay time until alerts on TO1,

TO2, UV and OV are reset. Leaving the pin open generates

a minimum delay of 500s. Capacitance on this pin adds

an additional 8ms/nF reset delay time. Tie TMR to VCC to

bypass the timer.

TO1: Temperature Logic Output 1. Open drain logic output

that pulls to GND when VPTAT crosses the threshold voltage

on pin VT1 with a polarity set by the PS pin (see Table 3

in Applications Information). When VPTAT crosses the

threshold voltage on pin VT1 with opposite polarity, an

additional hysteresis of 20mV is required to release TO1

high after a delay adjustable by the capacitor on TMR. TO1

has a weak 400k pull-up to VCC and may be pulled above

VCC using an external pull-up. Leave TO1 open if unused.

TO2: Temperature Logic Output 2. Open drain logic output

that pulls to GND when VPTAT crosses the threshold voltage

on pin VT2 with a polarity set by the PS pin (see Table 3

in Applications Information). When VPTAT crosses the

threshold voltage on pin VT2 with opposite polarity, an

additional hysteresis of 20mV is required to release TO2

high after a delay adjustable by the capacitor on TMR. TO2

has a weak 400k pull-up to VCC and may be pulled above

VCC using an external pull-up. Leave TO2 open if unused.

UV: Undervoltage Logic Output. Open drain logic output

that pulls to GND when either the voltage at VH1 or VH2

is below 0.5V. Held low for an adjustable delay time set

by the capacitor connected to pin TMR. UV has a weak

400k pull-up to VCC and may be pulled above VCC using

an external pull-up. Leave pin open if unused.

VCC: Supply Voltage. Bypass this pin to GND with a 0.1F

(or greater) capacitor. VCC operating range is 2.25V to 5.5V.

VH1, VH2: Voltage High Inputs 1 and 2. When the voltage

on either pin is below 0.5V, an undervoltage condition is

triggered. Tie pin to VCC if unused.

VL1, VL2: Voltage Low Inputs 1 and 2. When the voltage

on either pin is above 0.5V, an overvoltage condition is

triggered. Tie pin to GND if unused.

VPTAT: Proportional to Absolute Temperature Voltage

Output. The voltage on this pin is proportional to the

selected sensor’s absolute temperature. An internal or

external sensor is chosen with the DS pin. V

PTAT can

drive up to ±200A of load current and up to 1000pF of

capacitive load. For larger load capacitances insert a 1k

LTC2995

2995f

resistor between VPTAT and the load to ensure stability.

VPTAT is pulled low when the supply voltage goes below

the under voltage lockout threshold.

VREF: Voltage Reference Output. VREF provides a 1.8V

reference voltage. VREF can drive up to ±200A of load

current and up to 1000pF of capacitive load. For larger

load capacitances insert 1k between VREF and the load

to ensure stability. Leave VREF open if unused.

VT1: Temperature Threshold 1. When VPTAT crosses the

voltage on VT1 with a polarity set by the PS pin, TO1 is

pulled low. Tie VT1 to GND if unused.

VT2: Temperature Threshold 2. When VPTAT crosses the

voltage on VT2 with a polarity set by the PS pin, TO2 is

pulled low. Tie VT2 to VCC if unused.

PIN FUNCTIONS

BLOCK DIAGRAM

2995 BD

VH1 CH1

CH2

CL2

CT2

CT1

CL1

UVLO

VCC

VL1

VH2

VL2

VT2

VREF

VT1

VPTAT

–

1.3M

500k

0.5V

200k

200k

1.2V

1.8V

400k

UVLO

18 7D–D+

DS PS GND

619

T TO V

CONVERTER

TO1/TO2

PULSE

GENERATOR

UV PULSE

GENERATOR

OSCILLATOR

VCC

400k

TMR

VCC

400k

TO2

VCC

400k

TO1

VCC

400k

OV PULSE

GENERATOR

3 STATE

DECODE

3 STATE

DECODE

VCC

LTC2995

2995f

OPERATION

Overview

The LTC2995 combines the functionality of a temperature

measurement and monitor device with a dual voltage

supervisor. It provides a buffered voltage proportional to

the absolute temperature of either an internal or a remote

diode (VPTAT) and compares this voltage to thresholds that

can be set by external resistor dividers from the on-board

reference (VREF).

The LTC2995 also provides four voltage threshold

inputs that are continuously compared to an internal 0.5V

reference allowing two systems voltages to be monitored

for undervoltage and overvoltage conditions.

Diode Temperature Sensor

Temperature measurements are conducted by measuring

the voltage of either an internal or an external diode with

multiple test currents. The relationship between diode

voltage VD and diode current ID can be solved for absolute

Temperature in degrees Kelvin T:

⎛

⎝

⎜⎞

⎠

⎟

T=q

ηtktVD

ln ID

where IS is a process dependent factor on the order of

10–13A, η is the diode ideality factor, k is the Boltzmann

constant and q is the electron charge. This equation shows

a relationship between temperature and voltage dependent

on the process depended variable IS. Measuring the same

diode (with the same value IS) at two different currents

(ID1 and ID2) yields an expression independent of IS:

ln ID2

ID1

⎛

⎝

⎜⎞

⎠

⎟

T=q

ηtktVD2 –V

Series Resistance Cancellation

Resistance in series with the remote diode causes a positive

temperature error by increasing the measured voltage at

each test current. The composite voltage equals:

⎛

⎝

⎜⎞

⎠

⎟

VD+VERROR =ηkT

qtln ID

IS+RStID

The LTC2995 removes this error term from the sensor

signal by subtracting a cancellation voltage VCANCEL. A

resistance extraction circuit uses one additional current

measurement to determine the series resistance in the

measurement path. Once the correct value of the resistor is

determined, VCANCEL equals VERROR. Now the temperature

to voltage converter input signal is free from errors due

to series resistance.

LTC2995 can cancel series resistances up several hundred

ohms (see Typical Performance Characteristics curves).

Higher series resistances cause the cancelation voltage

to saturate.

LTC2995

2995f

Temperature Measurements

The LTC2995 continuously measures the sensor diode at

different test currents and generates a voltage proportional

to the absolute temperature of the sensor at the VPTAT pin.

The voltage at VPTAT is updated every 3.5ms.

The gain of VPTAT is calibrated to 4mV/K for the measure-

ment of the internal diode as well as for remote diodes

with an ideality factor of 1.004.

TKELVIN =VPTAT

4mV /K (η=1.004)

If an external sensor with an ideality factor different from

1.004 is used, the gain of VPTAT will be scaled by the ratio

of the actual ideality factor (ηACT) to 1.004. In these cases,

the temperature of the external sensor can be calculated

from VPAT by:

TKELVIN =VPTAT

4mV / K •1.004

ηACT

Temperature in degrees Celsius can be deduced from

degrees Kelvin by:

CELSIUS = TKELVIN – 273.15

The three-state diode select pin (DS) determines whether

the temperature of the external or the internal diode is

measured and displayed at VPTAT as described in Table 1.

Table 1. Diode Selection

DIODE LOCATION DS PIN

Internal VCC

External GND

Both Open

If the DS pin is left open, the LTC2995 measures both

diodes alternately and VPTAT changes every 30ms from the

voltage corresponding to the temperature of the internal

sensor to the voltage corresponding to the temperature

of the external sensor. If D+ is tied to VCC, the LTC2995

measures the internal diode regardless of the state of

the DS pin.

APPLICATIONS INFORMATION

Choosing an External Sensor

The LTC2995 is factory calibrated for an ideality factor of

1.004, which is typical of the popular MMBT3904 NPN

transistor. Semiconductor purity and wafer level process-

ing intrinsically limit device-to-device variation, making

these devices interchangeable between manufacturers

with a temperature error of typically less than 0.5°C. Some

recommended sources are listed in Table 2:

Table 2 Recommended Transistors for Use As Temperature

Sensors

MANUFACTURER PART NUMBER PACKAGE

Fairchild

Semiconductor

MMBT3904 SOT-23

Central

Semiconductor

CMBT3904 SOT-23

Diodes Inc. MMBT3904 SOT-23

On Semiconductor MMBT3904LT1 SOT-23

NXP MMBT3904 SOT-23

Infineon MMBT3904 SOT-23

Rohm UMT3904 SC-70

Discrete two terminal diodes are not recommended as

remote sensing devices as their ideality factor is typically

much higher than 1.004. Also MOS transistors are not

suitable as they don’t exhibit the required current to tem-

perature relationship. Furthermore gold doped transistors

(low beta), high frequency and high voltage transistors

should be avoided as remote sensing devices.

Connecting an External Sensor

The change in sensor voltage per °C is hundreds of

microvolts, so electrical noise must be kept to a mini-

mum. Bypass D+ and D– with a 470pF capacitor close to

the LTC2995 to suppress external noise. Recommended

shielding and PCB trace considerations for best noise

immunity are illustrated in Figure 1.

Figure 1. Recommended PCB Layout

D+

D–

LTC2995

2995 F01

GND

470pF

GND SHIELD TRACE

NPN SENSOR

LTC2995

2995f

D+

D–

470pF

LTC2995

2N3904

2995 F02

GND

APPLICATIONS INFORMATION

Leakage currents at D+ affect the precision of the remote

temperature measurements. 100nA leakage current leads

to an additional error of 2°C (see Typical Performance

Characteristics).

Note that bypass capacitors greater than 1nF will cause

settling time errors in the different measurement cur-

rents and therefore introduce an error in the temperature

measurement (see Typical Performance Characteristics).

The LTC2995 compensates series resistance in the

measurement path and thereby allows accurate remote

temperature measurements even with several meters of

distance between the sensor and the device. The cable

length between the sensor and the LTC2995 is only limited

by the mutual capacitance introduced between D+ and

D– which degrades measurement accuracy (see Typical

Performance Characteristics).

For example an AT6 cable with 50pF/m should be kept

shorter than ~20m to keep the capacitance less than 1nF.

To save wiring, the cathode of the remote sensor can

also be connected to remote GND and D– to local GND

as shown below.

components. Noise around odd multiples of 6kHz (±20%)is

amplified by the measurement algorithm and converted at

a DC offset in the temperature measurement (see Typical

Performance Characteristics).

The LTC2995 can withstand up to ±4kV of electrostatic

discharge (ESD, human body). ESD beyond this voltage

can damage or degrade the device including lowering the

remote sensor measurement accuracy due to increased

leakage currents on D+ or D–.

To protect the sensing inputs against larger ESD strikes,

external protection can be added using TVS diodes to

ground (Figure 3). Care must be taken to choose diodes

with low capacitance and low leakage currents in order

not to degrade the external sensor measurement accuracy

(see Typical Performance Characteristics curves).

The temperature measurement of the LTC2995 relies only

on differences between the diode voltage at multiple test

circuits. Therefore DC offsets smaller than 300mV between

remote and local GND do not impact the precision of the

temperature measurement. The cathode of the sensor

can accommodate modest ground shifts across a system

which is beneficial in applications where a good thermal

connectivity of the sensor to a device whose temperature

is to be monitored (shunt resistor, coil, etc.) is required.

Care must be taken if the potential difference between

the cathode and D– does not only content DC but also AC

Figure 2. Single Wire Remote Temperature Sensing

Figure 3. Increasing ESD Robustness with TVS Diodes

To make the connection of the cable to the IC polarity

insensitive during installation, two sensor transistors

with opposite polarity at the end of a two wire cable can

be used as shown on Figure 4.

Again, care must be taken that the leakage current of the

second transistor does not degrade the measurement

accuracy.

Figure 4. Polarity Insensitive Remote Diode Sensor

D+

D–

220pF

10 LTC2995

MMBT3904

PESD5Z6.0 2995 F03

GND

10

D+

D–

LTC2995

MMBT3904 470pF

2995 F04

GND

LTC2995

2995f

APPLICATIONS INFORMATION

Output Noise Filtering

The VPTAT output typically exhibits 0.6mV RMS (0.25°C

RMS) noise. For applications which require lower noise

digital or analog averaging can be applied to the output.

Choose the averaging time according to:

⎛

⎝

⎜⎞

⎠

⎟

tAVG =0.01[]

°CHz

TNOISE

where tAVG is the averaging time and TNOISE the desired

temperature noise in °C RMS. For example, if the desired

noise performance is 0.015°C RMS, set the averaging time

to one second. See Typical Performance Characteristics.

Temperature Monitoring

The LTC2995 continuously compares the voltage at VPTAT

to the voltages at the pins VT1 and VT2 to detect either an

overtemperature (OT) or undertemperature (UT) condition.

The VT1 comparator output drives the open-drain logic

output pin TO1 and the VT2 comparator output drives the

open-drain logic output pin TO2. The polarity of these

comparisons is configured via the three-state polarity

select pin (PS) (Table 3).

Table 3. Temperature Polarity Selection

PS PIN FUNCTION CONDITION OUTPUT

VCC

VT1 Undertemperature

Threshold VPTAT < VT1 TO1 Pulled Low

VT2 Overtemperature

Threshold VPTAT > VT2 TO2 Pulled Low

Open

VT1 Overtemperature

Threshold VPTAT > VT1 TO1 Pulled Low

VT2 Overtemperature

Threshold VPTAT > VT2 TO2 Pulled Low

GND

VT1 Undertemperature

Threshold VPTAT < VT1 TO1 Pulled Low

VT2 Undertemperature

Threshold VPTAT < VT2 TO2 Pulled Low

If pin PS is connected to VCC, the voltage on VT1 becomes

an undertemperature threshold and the voltage on VT2

an overtemperature threshold. In this configuration TO1 is

pulled low if the voltage VPTAT falls during five consecutive

conversions below the undertemperature threshold VT1.

Once pulled low, TO1 is released high again if VPTAT rises

above VT1 plus an additional hysteresis of about 20mV.

Accordingly, T02 is pulled low if the voltage VPTAT rises

above the overtemperature threshold VT2 and –once pulled

low– TO2 is released high if VPTAT falls below VT2 minus

an additional hysteresis of about 20mV. Leaving PS uncon-

nected configures both VT1 and VT2 as overtemperature

thresholds and connecting PS to GND configures them

both as undertemperature thresholds. If the internal and

external sensors are monitored alternately by leaving DS

unconnected, VT1 becomes a dedicated threshold for the

internal sensor and VT2 becomes a dedicated threshold

for the external sensor.

Temperature Monitor Design Example

The LTC2995 can be configured to give an early warning

if the temperature of the internal sensor rises above 60°C

and an alarm if the temperature passes 90°C. Tie the DS

pin to VCC to select the internal sensor and leave the pin

PS unconnected to configure both input voltages VT1 and

VT2 as overtemperature thresholds. The voltages at VT1

and VT2 are set to:

VT1 =(60K +273.15K) • 4mV

K=1.332V

VT2 =(90K +273.15K) • 4mV

K=1.452V

When VPTAT reaches the threshold voltage on pin VT1, TO1

is pulled low indicating an overtemperature early warning.

If the temperature reaches 90°C TO2 is also pulled low,

indicating an overtemperature alarm.

Once the temperature drops below each threshold, the

corresponding TO pins will return high after a time-out-

period (tUOTO) set by the capacitor connected to TMR.

LTC2995

2995f

D+DS

D–

1.2V

200k

400k

1.8V

VCC

VREF

RTC

VT2

VT1

VCC

VPTAT

TO2

TO1

3.3V

LTC2995

2995 F06

OT ALARM

OT WARNING

RTB

RTA

GND

–

TO1/TO2

PULSE

GENERATOR

UVLO

VCC

400k

VCC

400k

T/V

Figure 5. Temperature Thresholds

Figure 6. Monitoring Internal Temperature with Two Overtemperature Thresholds

APPLICATIONS INFORMATION

Temperature Thresholds

The threshold voltages at VT1 and VT2 can be set with

the 1.8V reference voltage (VREF) and a resistive divider

as shown in Figure 5.

The following design procedure can be used to size the

resistive divider.

1. Calculate Threshold Voltages:

VT1 =T1• 4mV

K•ηACT

1.004

VT2 =T2 • 4mV

K•ηACT

1.004

where ηACT denotes the actual ideality factor if an ex ternal

sensor is used and T1 and T2 are the desired threshold

temperatures in degrees Kelvin.

2. Choose RTA to obtain the desired VT1 threshold for

a desired current through the resistive divider

(IREF):

RTA =VT1

IREF

3. Choose RTB to obtain the desired VT2 threshold:

RTB =VT2 – VT1

IREF

2995 F05

VPTAT

RTC

RTB

RTA

VREF = 1.8V

1.8V

SLOPE = t



ACT

200k T1T2L

VT2

VT1

O.8V

LTC2995

2995f

APPLICATIONS INFORMATION

4. Finally RTC is determined by:

RTC =1.8V – VT2

IREF

In the Temperature Monitor example discussed earlier with

thresholds at VT1 = 60°C and VT2 = 90°C and a desired

reference current of 10A, the required values for RTA,

RTB and RTC can be calculated as:

RTA =1.332V

10µA =133.2k

RTB =1.452V – 1.332V

10µA =12k

RTC =1.8V – 1.452V

10µA =34.8k

Voltage Monitoring

In addition to temperature measurement, the LTC2995

features a low power dual voltage monitoring circuit. Each

voltage monitor has two inputs (VH1/VL1 and VH2/VL2)

for detecting undervoltage and overvoltage conditions. If

either VH1 or VH2 falls below 0.5V (typical), the LTC2995

communicates an undervoltage condition by pulling UV

low. Similar, an overvoltage condition is flagged by pulling

OV low if either VL1 or VL2 rises above 0.5V.

When configured to monitor a positive voltage Vn using

the 3-resistor circuit configuration shown in Figure 5,

VHn will be connected to the high side tap of the resistive

divider and VLn will be connected to the low side tap of

the resistive divider.

Voltage Monitor Design Procedure

The following 3-step design procedure selects appropriate

resistances to obtain the desired UV and OV trip points

for the voltage monitor circuit in Figure 7.

For supply monitoring, Vn is the desired nominal operat-

ing voltage, In is the desired nominal current through the

resistive divider, VOV is the desired overvoltage trip point,

and VUV is the desired undervoltage trip point.

1. RA is chosen to set the desired trip point for the

overvoltage monitor:

RA=0.5V

•VN

VOV

(1)

2. Once RA is known, RB is chosen to set the desired

trip point for the undervoltage monitor:

RB=0.5V

•VN

VUV

–RA

(2)

3. Once, RA and RB are known, RC is determined by:

RC=VN

–RA–R

(3)

Voltage Monitor Example

A typical voltage monitor application is shown in Figure 2.

The monitored voltage is a 5V ±10% supply. Nominal

current in the resistive divider is 10µA.

1. Find RA to set the OV trip point of the monitor:

RA=0.5V

10µA •5V

5.5V ≈45.3k

Figure 7. 3-Resistor Positive UV/OV Monitoring

–

–0.5V

LTC2995

UVn

VHn

2995 F07

VLn

OVn

LTC2995

2995f

APPLICATIONS INFORMATION

2. Find RB to set the UV trip point of the monitor:

RB=0.5V

10µA •5V

4.5V – 453 ≅10k

3. Determine RC to complete the design:

RC=5V

10µA –453Ω– 100Ω≈442k

Power-Up and Undervoltage Lockout

As soon as V

CC reaches approximately 1V during

power-up, the OV as well as TO1 and TO2 we ak l y p ul l t o VCC

while the UV output asserts low indicating an undervolt-

age lockout condition. Above VCC = 2V (typical), the VH

and VL inputs take control. Once both VH inputs and VCC

are valid, an internal timer is started. After an adjustable

delay time, UV weakly pulls high.

When VCC falls below 1.9V, the LTC2995 indicates again

an undervoltage lockout (UVLO) condition by pulling low

UV while OV is cleared.

Threshold Accuracy

Reset threshold accuracy is important in a supply sensitive

system. Ideally, such a system would only reset if supply

voltages fell outside the exact threshold for a specified

margin. All LTC2995 VHn/VLn inputs have a relative

threshold accuracy of ±1.5% over the full operating

temperature range. For example, when the LTC2995 is

configured to monitor a 5V input with a 10% tolerance,

the desired UV trip point is 4.5V. Because of the ±1.5%

relative accuracy of the LTC2995, the UV trip point can be

anywhere between 4.433V and 4.567V which is 4.5V ±1.5%.

Likewise, the accuracy of the resistances chosen for RA,

RB, and RC can affect the UV and OV trip points as well.

Using the previous example, if the resistances used to set

the UV trip point have 1% accuracy, the UV trip range can

grow to between 4.354V and 4.650V. This is illustrated in

the following calculations.

The UV trip point is given as:

VUV =0.5V t1+RC

RA+RB

⎛

⎝

⎜⎞

⎠

⎟

The two extreme conditions, with a relative accuracy of

1.5% and resistance accuracy of 1%, result in:

VUV(MIN) =0.5V t0.985 t1+RCt0.99

(RA+RB)t1.01

⎛

⎝

⎜⎞

⎠

⎟

and

VUV(MAX) =0.5V t1.015 t1+RCt1.01

(RA+RB)t0.99

⎛

⎝

⎜⎞

⎠

⎟

For a desired trip point of 4.5V,

RA+RB

Therefore,

VUV(MIN) =0.5V t0.985 t1+80.99

1.01 =4.3545V

⎛

⎝

⎜⎞

⎠

⎟

and

VUV(MAX) =0.5V t1.015 t1+81.01

0.99 =4.650V

⎛

⎝

⎜⎞

⎠

⎟

Glitch Immunity

In any supervisory application, noise on the monitored DC

voltage can cause spurious resets. To solve this problem

without adding hysteresis to the VH/VL comparators, which

would add error to the trip voltage, the LTC2995 lowpass

filters the output of the comparator. This filter causes the

output of the comparator to be integrated before assert-

ing the UV or OV logic. Any transient at the input of the

comparator must be of sufficient magnitude and duration

before the comparator will trigger the output logic. The

Typical Performance Characteristics section shows a graph

of the Typical Transient Duration vs Comparator Overdrive.

In temperature monitoring, the voltage at VPTAT must

exceed a threshold for five consecutive temperature up-

date intervals before the respective TO pin is pulled low.

Once the VPTAT voltage crosses back the threshold with

an additional 20mV of hysteresis, the respective TO pin

is released after a single update interval and an additional

delay adjustable by the capacitor on TMR.

LTC2995

2995f

Timing of Alert Outputs

The LTC2995 has an adjustable timeout period (tUOTO)

that holds UV, OV, TO1 or TO2 asserted after any faults

have cleared. This delay will minimize the effect of input

noise with a frequency above 1/tUOTO.

A voltage monitoring example: When any VH drops below

its threshold, the UV pin asserts low. When all VH inputs

recover above their thresholds, the output timer starts. If

all inputs remain above their thresholds when the timer

finishes, the UV pin weakly pulls high. However, if any

input falls below its threshold during this timeout period,

the timer resets and restarts when all inputs are again

above the thresholds.

A temperature monitoring example: Tying PS to VCC

configures TO2 as overtemperature output. In case of

an overtemperature condition pin TO2 asserts low. The

output timer starts when the temperature crosses back

below the threshold minus the temperature hysteresis If

the temperature remains below the threshold, the timer

finishes and pin TO2 releases high.

Selecting the Timing Capacitor

The timeout period (tUOTO) for the LTC2995 is adjustable in

order to accommodate a variety of applications. Connect-

ing a capacitor, CTMR, between the TMR pin and ground

sets the timeout period. The value of capacitor needed for

a particular timeout period is:

CTMR =tUOTO –0.5ms

8[ms / nF]

The Reset Timeout Period vs Capacitance graph found in

the Typical Performance Characteristics section shows the

desired delay time as a function of the value of the timer

capacitor that should be used. Leaving the TMR pin open

with no external capacitor generates a timeout period of

approximately 500s. For long timeout periods, the only

limitation is the availability of a large value capacitor with

low leakage. Capacitor leakage current must not exceed

the minimum TMR charging current of 1.5A.

Tying the TMR pin to VCC will bypass the timeout period

and no delay will occur.

Digital Output Characteristics

The DC characteristics of the UV, OV, TO1 and TO2 pull-up

and pull-down strength are shown in the Typical Perfor-

mance Characteristics section. Each pin has a weak 400k

internal pull-up to VCC and a strong pull-down to ground

and can be pulled above VCC.

This arrangement allows these pins to have open-drain

behavior while possessing several other beneficial char-

acteristics. The weak pull-up eliminates the need for an

external pull-up resistor when the rise time on the pin is

not critical. On the other hand, the open drain configuration

allows for wired-OR connections and can be useful when

more than one signal needs to pull-down on the output.

At VCC = 1V, the weak pull-up current is barely turned on.

Therefore, an external pull-up resistor of no more than

100k is recommended on the pin if the state and pull-up

strength of the pin is crucial at very low VCC.

Note however, by adding an external pull-up resistor, the

pull-up strength on the pin is increased. Therefore, if it

is connected in a wired-OR connection, the pull-down

strength of any single device needs to accommodate this

additional pull-up strength.

Output Rise and Fall Time Estimation

The UV, OV, TO1 and TO2 outputs have strong pull-down

capability. The following formula estimates the output fall

time (90% to 10%) for a particular external load capaci-

tance (CLOAD):

FALL ≈ 2.2 • RPD • CLOAD

where RPD is the on-resistance of the internal pull-down

transistor estimated to be typically 40 at VDD > 1V and

at room temperature (25°C), and CLOAD is the external

load capacitance on the pin. Assuming a 150pF load

capacitance, the fall time is about 13ns. The rise time on

the UV, OV, TO1 and TO2 pins is limited by a 400k pull-up

resistance to VDD. A similar formula estimates the output

rise time (10% to 90%):

RISE ≈ 2.2 • RPU • CLOAD

where RPU is the pull-up resistance.

APPLICATIONS INFORMATION

LTC2995

2995f

±10% Voltage Monitor (1.8V and 2.5V) and Internal/Remote Overtemperature Monitor

TYPICAL APPLICATIONS

±20% Voltage Monitor (12V and 5V) and 0°C to 70°C Internal UT/OT Monitoring with Common

Temperature and Powergood LED

POWER

SUPPLIES

TEMPERATURE AND

POWER GOOD LED

VH1

VL1

VH2

VL2

D+

D–

LTC2995

442k

113k

12V

41.2k

2995 TA03

VT1VT2

43k 28k 110k

OT T > 70°C

UT T < 0°C

+20%

–20%

GND TMRVREF

4.12k

2.15k

21.5k

VPTAT

TO2

TO1

VCC

0.1µF 2.15k

VH1

VL1

VH2

VL2

D+

D–

LTC2995

194k

124k

2.5V

1.8V

45.3k

2995 TA02

VT1VT2

20k 20k 140k

OT T > 125°C FOR EXTERNAL SENSOR

MMBT390

OT T > 75°C FOR INTERNAL SENSOR

+10%

–10%

GND TMRVREF

45.3k

10.2k

VPTAT

TO2

TO1

VCC

5nF

470pF

0.1µF

POWER

SUPPLIES

LTC2995

2995f

TYPICAL APPLICATIONS

Celsius Thermometer and ±10% Voltage Monitor (1.8V and 2.5V)

±10% Voltage Monitor (12V and 5V) and –20°C to 70°C Internal UT/OT Monitor with

Manual Undervoltage Reset Button

POWER

SUPPLIES

VH1

VL1

VH2

VL2

D+

D–

LTC2995

44.2k

115k

12V

4.53k VT1VT2

43k 36k 102k

OT T > 70°C

UT T < –20°C

+10%

–10%

GND TMRVREF

4.53k

MANUAL

RESET BUTTON

(NORMALLY OPEN)

VPTAT

TO2

TO1

VCC

0.1µF

SYSTEM

RESET

2995 TA05

POWER

SUPPLIES

VH1

VL1

VH2

VL2

D+

D–

LTC2995

194k

124k

2.5V

1.8V

45.3k

2995 TA04

VT1VT2

+10%

–10%

1.8V 100k

4mV/K

GND TMR TO2 TO1

45.3k

10.2k

VPTAT

VCC

0.1µF

5nF

470pF MMBT3904

VREF

–

62k

143k 1µF

0.1µF

LTC1150

–5V

10mV/°C

0V AT 0°C

150k 1.8k

LTC2995

2995f

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibilit y is assumed for its use. Linear Technology Corporation makes no representa-

t i o n t h a t t h e i n t e r c o n n e c t i o n o f i t s c i r c u i t s a s d e s c r i b e d h e r e i n w i l l n o t i n f r i n g e o n e x i s t i n g p a t e n t r i g h t s .

PACKAGE DESCRIPTION

3.00 ± 0.10

(4 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

1.65 ± 0.05

NOTE:

1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

PIN 1

TOP MARK

(NOTE 6)

0.40 ± 0.10

BOTTOM VIEW—EXPOSED PAD

1.65 ± 0.10

(4-SIDES)

0.75 ± 0.05 R = 0.115

TYP

R = 0.05

TYP

0.20 ± 0.05

PIN 1 NOTCH

R = 0.20 TYP

OR 0.25 × 45°

CHAMFER

19 20

0.40 BSC

0.200 REF

2.10 ± 0.05

3.50 ± 0.05

(4 SIDES)

0.70 ±0.05

0.00 – 0.05

(UD20) QFN 0306 REV A

0.20 ±0.05

0.40 BSC

PACKAGE

OUTLINE

UD Package

20-Lead Plastic QFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1720 Rev A)

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

LTC2995

2995f

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT 0412 • PRINTED IN USA

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One Adjustable

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One Adjustable

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Adjustable)

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2 ADJ Inputs, Monitors Negative Voltages

LTC2912 Single UV/OV Positive Voltage Monitor Separate VCC Pin, 8-Lead TSOT and 3mm × 2mm DFN Packages

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Dual OV/UV ±10% Supply and 75°C/125°C OT/OT Remote Temperature Monitor

ASIC/

CPU/

FPGA

VH1

VL1

VH2

VL2

D+

D–

LTC2995

194k

64.4k

2.5V

1.2V

45.3k

2995 TA06

VT1 VT2 VREF

+10%

–10%

GNDTMR

45.3k

10.2k

VPTAT

TO2

TO1

VCC

0.1µF

5nF 140k 20k 20k

470pF

OT T > 125°C

OT T > 75°C

A/D